Well Japan doesn't have such a horrific human and civil rights record over the past 60 years.
And ditto on the women.
Japan! However it's extremely expensive (like mentioned). I'm of chinese ethnicity though so this might be a bit biased as I would prefer visiting a different country :P
Indeed, every country has its own unique charm. Both countries are worth you to visit. It depends on what you are interested in. I have lots of Chinese and Japanese friends, they all very good. However, if I were you, and only one country could be visited at the moment, I would like to choose to travel in China anyway. Firstly, China has a longer history, also it has lots of different national minorities, which can reflect different cultures. Secondly, either Shanghai or Beijing even HK, they are just one part of China, where are familiar with foreigners. So if you want to see some different but original culture, Xian, Nanjing,Chongqing, Tibet would be good places. Last but not least, some Japanese culture we are familiar with are mostly developed from ancient China, so why not go to China and directly see.
However, no matter where you would go, hope you have a good journey.